1. Field of the Invention
The present invention relates to the debromination of dibrominated naphthol compounds, and, more especially, to a process for the monodebromination of dibrominated naphthol compounds of formula (1): ##STR1## by regioselective catalytic hydrodebromination,
The particularly desired reaction products prepared by the subject debromination process of the invention have the formula (2): ##STR2##
2. Description of the Prior Art
6-Bromo-2-hydroxynaphthalene (also named 6-bromo-.beta.-naphthol) of formula (2) above is a known compound that is particularly advantageous and valuable. It is in fact used for the synthesis of 6-bromo-2-methoxynaphthalene (via alkylation by means of dimethyl sulfate or methanol), the latter compound being widely used for the production of naproxen or nabumetone, which are well-known anti-inflammatory drugs, or even methallenestril, which is an estrogen (compare, for example, the Merk Index, eleventh edition, pages 1002, 1014 and 937 (1989)).
EP-A-179,447 describes the preparation of 6-bromo-2hydroxynaphthalene by stoichiometric metallic reduction of 1,6-dibromo-2-hydroxynaphthalene, according to the following reaction scheme: ##STR3## wherein M is a reducing metal, such as iron or tin, and the above dibrominated compounds may themselves be prepared simply by direct bromination or .beta.-naphthol, as follows: ##STR4##
However, the reduction of dibrominated naphthol compounds to monobrominated derivatives via a process such as that described above presents the disadvantage, inter alia, of requiring a significant consumption of metal, metal which moreover reappears in the form of a waste effluent which is difficult to recover and which is sometimes polluting, such as, for example, FeBr.sub.2.
In addition, the reaction yields of desired monobrominated derivatives by such a process may prove to be insufficient.